Nb3Sn conductors have been made which incorporate ZrO2 artificial pinning centers (APCs) that serve to refine the grain size of the superconducting material. Work on these wires has resulted in conductors which approach the FCC specification of Jc of 1500 A/mm2 at 16 T and 4.2 K. Understanding the causes of high Jc at mid to high magnetic fields in these wires is crucial for developing an optimum conductor for next-generation particle accelerators. Reduced grain size has been demonstrated to increase Jc, due to the increased flux pinning at grain boundaries. In addition, ZrO2 particles serve as point-like flux pinning centers, with a different behavior versus magnetic field. The relative contribution of these two factors on the Jc is evaluated. The effect of stoichiometry on the increased Birr and Bc2 in ternary APC wires is also considered.